1. Field of the Invention:
This invention relates to a television receiver in which anytime in the existence of a closed-caption signal in an image signal of television broadcast, a display allowing the user to recognize the closed-caption signal can be made on the screen. Also the invention concerns a closed-caption-broadcast decoder for sampling a closed-caption signal to an image signal of television broadcast for mixing therewith and for outputting the composite signal to an external television receiver.
2. Description of the Related Art:
In North America, for people who cannot understand English and people who have difficulty in hearing, closed-caption broadcast, displaying closed caption on the screen of television broadcast, has been standardized and set about in recent years. Since this closed-caption broadcast adopts a transmission method in which character data are superposed in a vertical retrace time and are displayed on the screen, the closed-caption broadcast can coexist with the existing television broadcast. The closed-caption broadcast by this method requires a special decoder. Consequently it is necessary to connect a decoder, for closed-caption broadcast, to the external television receiver; no television receiver with a built-in decoder for closed-caption broadcast is known at the present time.
FIG. 3 of the accompanying drawings is a block diagram showing the circuit of a conventional television receiver in which a closed-caption signal demodulator of the known type is mounted. In FIG. 3, reference numeral 1 designates an image signal; 2, a closed-caption signal demodulating unit; 3, a closed-caption signal to be output from the closed-caption signal demodulating unit 2; 4, a mixer for mixing the image signal 1 and the closed-caption signal 3; 5, a microcomputer for controlling the closed-caption signal demodulating unit 2; and 6, a control signal to be output from the microcomputer 5.
The closed-caption signal demodulating unit 2 includes a character memory (storage) 11 containing data of the closed-caption signal 3, a closed-caption signal demodulator 9, and an output circuit 10 for outputting the closed-caption signal 3 to the mixer 4. A decoder for mixing a closed-caption signal and an image signal and outputting the composite signal to the external television receiver also has the same construction.
The operation of this television receiver will now be described. The input image signal 1 is divided into two parts, one to be input to the closed-caption signal demodulator 9 of the closed-caption signal demodulating unit 2 and the other to be input to the mixer 4.
In this television receiver, when closed-caption signal demodulation is selected by the user, a control signal 6 meaning "closed-caption signal demodulation is needed" is sent from the microcomputer 5 to the closed-caption signal demodulating unit 2, whereupon the closed-caption signal demodulator 9 will demodulate a code signal 12 for obtaining a closed-caption signal 3 from an image signal 1. Then a character signal 14 corresponding the code signal 12 is read from the character memory 11 and is sent to the output circuit 10.
The output circuit 10 outputs to the mixer 4 the character signal 14, which is output from the character memory 11, as the closed-caption signal 3. Then the mixer 4 mixes the image signal 1 and the closed-caption signal 3, and the composite signal is displayed on the screen of the television receiver (not shown).
The foregoing description concerning the operation of the television receiver in which the closed-caption signal demodulating unit is mounted can be also applied to the operation of a closed-caption-broadcast decoder to be connected to an external television receiver.
However, with the foregoing arrangements of this invention, since a closed-caption signal will not be demodulated unless the user selects closed-caption display, he/she cannot recognize, before selection, whether or not there closed-caption broadcast in the television broadcast is included.